Topical Sensitizers in Alopecia Areata

Amy J. McMichael; Robert L. Henderson, Jr.


Dermatology Nursing. 2004;16(4) 

In This Article

Immunology of Topical Sensitizers

Sensitizers include any chemical for which the body develops immunity when exposed. Upon subsequent exposure, an inflammatory response is mounted by the immune system to fight off the chemical. Sensitizers can therefore include a wide range of chemicals and are not necessarily limited to those used in medical therapeutics. Perhaps one of the best known sensitizers is urushiol which is found in poison ivy and poison oak species. Whereas urushiol has little utility in medical therapeutics, other sensitizers do have certain properties that allow their use in treating dermatologic conditions such as AA.

Topical sensitization for treating AA relies on four characteristics of the sensitizer for efficacy: predictable immunomodulation (sensitization of the immune system), absence from the natural environment, lack of cross-reactivity with other substances, and, of course, safety. The absence of the sensitizer from the natural environment is important, or the sensitized individual may experience contact allergy from exposure during routine daily life activities.

Many theories exist for the mechanism of efficacy of sensitizers in AA, and research is lacking to validate them. However, one of the more popular views is that they redirect the inflammatory response in AA away from the hair follicle and direct it towards the exogenous chemical sensitizer (Happle, 1980). But the true mechanism is likely not so simplistic and cannot explain the regrowth that is sometimes observed at distant sites or on opposite sides from sensitizer application (castling phenomenon) suggesting a systemic action (Micali, Cicero, Nasca, & Sapuppo, 1996).


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